Assembling colloidal particles under oscillatory electric field (OEF) has become an emerging bottom-up technique to synthesize advanced materials and fabricate micro/nano devices. Surfactants have often been used in colloidal dispersions to improve their stability. However, the precise role of surfactants in particle assembly processes under OEF is unknown. Here, we systematically study the effects of ionic surfactants on the colloidal particle assembly process subject to a fixed OEF, by using an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (cetyltrimethylammonium bromide). In the concentration range below the critical micelle concentration (CMC), the particles tend to form three different aggregate structures, including randomly close-packed, hexagonally close-packed crystals, and randomly non close-packed structures. In the concentration range at CMC and above, the particles cannot assemble into any aggregate structures under the given OEF. With increasing surfactant concentration, the average interparticle separation distance within the aggregate can be regulated in a wide range. We qualitatively interpret the observed variation of particle assembly behaviors in different surfactant solutions based on the particle/particle interaction energy, implying that the repulsive electric double-layer interaction is significantly enhanced with increasing ionic surfactant concentration and hinders the particles approaching close to the high-energy barrier. These results suggest that the particle aggregate structure and interparticle separation distance of the two-dimensional colloidal assembly can be manipulated by controlling the ionic surfactant concentration according to the requirements of practical applications.

在振荡电场 (OEF) 下组装胶体粒子已成为合成先进材料和制造微/纳米器件的一种新兴的自下而上的技术。表面活性剂经常用于胶体分散体以提高其稳定性。然而，表面活性剂在 OEF 下颗粒组装过程中的确切作用尚不清楚。在这里，我们通过使用阴离子表面活性剂（十二烷基硫酸钠）和阳离子表面活性剂（十六烷基三甲基溴化铵）系统地研究了离子表面活性剂对固定 OEF 下胶体颗粒组装过程的影响。在临界胶束浓度（CMC）以下的浓度范围内，颗粒倾向于形成三种不同的聚集结构，包括随机密堆积、六边形密堆积晶体和随机非密堆积结构。在 CMC 及以上的浓度范围内，粒子无法在给定的 OEF 下组装成任何聚集结构。随着表面活性剂浓度的增加，聚集体内的平均颗粒间距可在较宽的范围内调节。我们根据粒子/粒子相互作用能定性地解释了观察到的不同表面活性剂溶液中粒子组装行为的变化，这意味着排斥双电层相互作用随着离子表面活性剂浓度的增加而显着增强，并阻碍粒子接近高-能量屏障。